Many diseases influence tissue displacement and related biomarker parameters, such as strain, twist, and torsion. Quantitative assessment of these parameters is of growing importance. Particularly, quantitative imaging of motion and strain in the cardiovascular system is an emerging field as being able to understand and measure the complex moving and contraction patterns of the heart and vessels can be helpful in both research and clinical settings.
Conventional applications include ischemia detection and evaluation of myocardial mechanics related to cardiac surgery. Newer applications include quantifying mechanical dyssynchrony in heart failure and measuring the functional effects of experimental therapies such as stem cell infusion. Other applications outside of the heart include assessment of vessel wall deformation and stretching.
Magnetic resonance imaging (MRI) has been a powerful tool for studying displacement and motion. Displacement Encoding with Stimulated Echoes (DENSE) is an Mill technique for quantitative imaging of tissue motion. This technique encodes tissue displacement into the phase of the magnetic resonance (MR) signal. Displacement or motion values can be extracted from the MR phase images for each displacement encoded direction, and combined to generate a displacement map. The displacement values can be further used to calculate the deformation and mechanics indices including but not limited to strain, twist, and torsion. When cine DENSE images are acquired, i.e., DENSE data at multiple cardiac phases, dynamic or time-resolved information about motion patterns can be further evaluated.
It is preferable to have DENSE images free of blood signal inside the left ventricle chambers or the vessel lumen, as the myocardial tissue or vessel wall is typically the region of interest, not the blood as its displacement is too large. In addition, if blood signal exists in the images, the signal can cause difficulties in delineating the boundaries of the myocardial chamber and vessel lumen, leading to errors in the final resultant images.
This document describes a method and apparatus for suppressing the residual blood signal in the early cardiac phases of the cine DENSE images, providing a dark-blood appearance for the entire cardiac cycle, thus allowing for more accurate quantitative time-resolved assessment of tissue displacement and related biomarker parameters.